1. Elevated levels of cytokines, especially interleukin (IL)_6 and IL_1ra, can be measured in the plasma of athletes after exhaustive long term exercise. 2. The present study investigates the kinetics of several cytokines and chemokines in ten male athletes before, during and after 2·5 h of treadmill running at 75% of maximal oxygen consumption (VOµ,max). Blood was sampled before, every half-hour during running and every hour in the following 6 h recovery period. 3. The plasma concentration of IL_6 increased after 30 min of running, and peaked at the end of running with a 25-fold increase compared with the pre-exercise value. IL_1ra increased only after running, and peaked after 2 h of rest with an 18-fold increase compared with the pre-exercise value. No changes were found in the concentrations of IL_1â, tumour necrosis factor (TNF)á, IL_15 and macrophage inflammatory protein (MIP)_1â, and the concentrations of IL_8 and MIP_1á were below detection limits. 4. The results suggest that very early events in exercise trigger the release of IL_6, and that the cytokine response to exercise has similarities to that observed after trauma.

The metabolic role of 5ЈAMP-activated protein kinase (AMPK) in regulation of skeletal muscle metabolism in humans is unresolved. We measured isoform-specific AMPK activity and ␤-acetyl-CoA carboxylase (ACC␤) Ser 221 phosphorylation and substrate balance in skeletal muscle of eight athletes at rest, during cycling exercise for 1 h at 70% peak oxygen consumption, and 1 h into recovery. The experiment was performed twice, once in a glycogen-loaded (glycogen concentration ϳ900 mmol/kg dry wt) and once in a glycogendepleted (glycogen concentration ϳ160 mmol/kg dry wt) state. At rest, plasma long-chain fatty acids (FA) were twofold higher in the glycogen-depleted than in the loaded state, and muscle ␣1 AMPK (160%) and ␣2 AMPK (145%) activities and ACC␤ Ser 221 phosphorylation (137%) were also significantly higher in the glycogen-depleted state. During exercise, ␣2 AMPK activity, ACC␤ Ser 221 phosphorylation, plasma catecholamines, and leg glucose and net FA uptake were significantly higher in the glycogen-depleted than in the glycogen-loaded state without apparent differences in muscle high-energy phosphates. Thus exercise in the glycogen-depleted state elicits an enhanced uptake of circulating fuels that might be associated with elevated muscle AMPK activation. It is concluded that muscle AMPK activity and ACC␤ Ser 221 phosphorylation at rest and during exercise are sensitive to the fuel status of the muscle. During exercise, this dependence may in part be mediated by humoral factors.acetyl-CoA carboxylase; glycogen; fatty acids; catecholamines IN HUMANS, 5ЈAMP-ACTIVATED PROTEIN KINASE (AMPK) is stimulated in skeletal muscle during exercise, and the degree of activation is dependent on the exercise intensity (5,14,32,59). In rodent muscle, pharmaceutical activation of AMPK by 5-aminoimidazole-4-carboxamide (AICA)-riboside leads to GLUT4 recruitment to the surface membrane and a stimulation of glucose transport that is additive to the effect of insulin but not to contraction (22,28). In addition, contraction-stimulated glucose transport and AMPK activity covary with time in incubated skeletal muscle (33). On the basis of these findings, it is hypothesized that AMPK is a mediator of contraction-stimulated glucose transport (16,22,28). However, recent studies in muscle from mice that express a dominant inhibitory mutant of ␣-AMPK show that a substantial part of contraction-induced glucose transport in vitro is AMPK independent, whereas AICA-riboside-and hypoxia-induced transport is totally dependent on AMPK activation (31, 45). In accordance, rodent studies have revealed conditions under which muscle glucose transport by these stimuli is increased in response to contraction without concurrent AMPK activation (10). Furthermore, energy-depleting stimuli, such as 2,4-dinitrophenol and hyperosmolarity, increase AMPK activity and glucose transport in L6 cells and skeletal muscle (21,40). However, the increase in glucose transport, but not the AMPK activation, is inhibited by calcium chelation and protein kinase C inhibition ...

The 5AMP-activated protein kinase (AMPK) is a potential antidiabetic drug target. Here we show that the pharmacological activation of AMPK by 5-aminoimidazole-1-␤-4-carboxamide ribofuranoside (AICAR) leads to inactivation of glycogen synthase (GS) and phosphorylation of GS at Ser 7 (site 2). In muscle of mice with targeted deletion of the ␣2-AMPK gene, phosphorylation of GS site 2 was decreased under basal conditions and unchanged by AICAR treatment. In contrast, in ␣1-AMPK knockout mice, the response to AICAR was normal. Fuel surplus (glucose loading) decreased AMPK activation by AICAR, but the phosphorylation of the downstream targets acetyl-CoA carboxylase-␤ and GS was normal. Fractionation studies suggest that this suppression of AMPK activation was not a direct consequence of AMPK association with membranes or glycogen, because AMPK was phosphorylated to a greater extent in response to AICAR in the membrane/glycogen fraction than in the cytosolic fraction. Thus, the downstream action of AMPK in response to AICAR was unaffected by glucose loading, whereas the action of the kinase upstream of AMPK, as judged by AMPK phosphorylation, was decreased. The fact that ␣2-AMPK is a GS kinase that inactivates GS while simultaneously activating glucose transport suggests that a balanced view on the suitability for AMPK as an antidiabetic drug target should be taken. Diabetes 53:3074 -3081, 2004 T he 5ЈAMP-activated protein kinase (AMPK) system is a sensor of cellular energy status that adjusts the supply of ATP to the demand for the nucleotide (1). Activation of ␣2-AMPK stimulates muscle glucose transport (2,3). Once glucose has been taken up and converted to glucose-6-phosphate (G6P), it can be stored as glycogen or metabolized by glycolysis to generate ATP. It has been reported that AMPK phosphorylates muscle glycogen synthase (GS) in cell-free assays at site 2 (Ser 7) (4). Thus, AMPK activation may under some conditions decrease the potential for glycogen synthesis. Recently, we and others showed that GS activity decreases in response to acute 5-aminoimidazole-1-␤-4-carboxamide ribofuranoside (AICAR) treatment of muscle-like cells in culture (5), isolated and perfused skeletal muscle (6 -8), and fast twitch, but not slow twitch, muscle in vivo (7). AICAR treatment leads to decreased gel mobility of GS in perfused muscle, which together with the decreased activity, is reversed by protein phosphatase treatment (6). These observations indicate that regulation of GS activity by AICAR involves phosphorylation of GS. Although it has been suggested that AICAR-induced GS deactivation is mediated by AMPK due to the negative correlation between ␣2-AMPK and GS activity (6), these data do not prove a causal relation. Thus, by studying muscle from ␣-AMPK knockout (KO) mice in the present study, we aimed to verify that AMPK is a muscle GS kinase in vivo.AMPK activity decreases when muscle is exposed to fuel surplus. For example, glucose loading and glycogen accumulation suppress muscle AMPK phosphorylation/ activation at basal co...

The protein and mRNA levels of several muscle lipid-binding proteins and the activity and mRNA level of muscle lipoprotein lipase (mLPL) were investigated in healthy, nonobese, nontrained (NT), moderately trained, and endurance-trained (ET) women and men. FAT/CD36 protein level was 49% higher (P < 0.05) in women than in men, irrespective of training status, whereas FAT/CD36 mRNA was only higher (P < 0.05) in women than in men in NT subjects (85%). Plasma membrane-bound fatty acid binding protein (FABPpm) content was higher in ET men compared with all other groups, whereas training status did not affect FABPpm content in women. FABPpm mRNA was higher (P < 0.05) in NT women than in ET women and NT men. mLPL activity was not different between gender, but mLPL mRNA was 160% higher (P < 0.001) in women than in men. mLPL activity was 48% higher (P < 0.05) in ET than in NT subjects, irrespective of gender, in accordance with 49% higher (P < 0.05) mLPL mRNA in ET than in NT subjects. A 90-min exercise bout induced an increase (P < 0.05) in FAT/CD36 mRNA (approximately 25%) and FABPpm mRNA (approximately 15%) levels in all groups. The present study demonstrated that, in the NT state, women had higher muscle mRNA levels of several proteins related to muscle lipid metabolism compared with men. In the ET state, only the gender difference in mLPL mRNA persisted. FAT/CD36 protein in muscle was higher in women than in men, irrespective of training status. These findings may help explain gender differences in lipid metabolism and, furthermore, suggest that the balance between gene transcription, translation, and possibly breakdown of several proteins in muscle lipid metabolism depend on gender.

5'-AMP-activated protein kinase (AMPK) has been proposed to be a pivotal factor in cellular responses to both acute exercise and exercise training. To investigate whether protein levels and gene expression of catalytic (alpha(1), alpha(2)) and regulatory (beta(1), beta(2), gamma(1), gamma(2), gamma(3)) AMPK subunits and exercise-induced AMPK activity are influenced by exercise training status, muscle biopsies were obtained from seven endurance exercise-trained and seven sedentary young healthy men. The alpha(1)- and alpha(2)-AMPK mRNA contents in trained subjects were both 117 +/- 2% of that in sedentary subjects (not significant), whereas mRNA for gamma(3) was 61 +/- 1% of that in sedentary subjects (not significant). The level of alpha(1)-AMPK protein in trained subjects was 185 +/- 34% of that in sedentary subjects (P < 0.05), whereas the levels of the remaining subunits (alpha(2), beta(1), beta(2), gamma(1), gamma(2), gamma(3)) were similar in trained and sedentary subjects. At the end of 20 min of cycle exercise at 80% of peak O(2) uptake, the increase in phosphorylation of alpha-AMPK (Thr(172)) was blunted in the trained group (138 +/- 38% above rest) compared with the sedentary group (353 +/- 63% above rest) (P < 0.05). Acetyl CoA-carboxylase beta-phosphorylation (Ser(221)), which is a marker for in vivo AMPK activity, was increased by exercise in both groups but to a lower level in trained subjects (32 +/- 5 arbitrary units) than in sedentary controls (45 +/- 1 arbitrary units) (P < 0.01). In conclusion, trained human skeletal muscle has increased alpha(1)-AMPK protein levels and blunted AMPK activation during exercise.